Telescoping is a process by which a roll of plastic film, initially cylindrical in shape, encounters an imbalance of forces causing the core and inner film layers to slide to one side or the other relative to the outer layers. This is also known as "coning," since the film roll takes on a shape resembling a telescope or cone, with the core and innermost film layers representing the apex of the cone (see FIGS. 1 and 2).
A number of factors are believed to cause telescoping. For example, films containing liquid additives and/or tackifiers (whether or not liquid) will often telescope when exposed to high (e.g. summertime) storage temperatures for extended periods of time. The liquid additives and/or tackifiers behave essentially as lubricants at elevated temperatures, causing a reduction in friction between the film layers. Furthermore, temperature-induced expansion of the film material can cause "squeezing" of the core and of the inner film layers.
Other factors which contribute to telescoping include nonuniform tension or misalignment of the film roll caused by imperfect winding, excessive levels of liquid additives at any temperatures, excessive levels of low molecular weight materials, and rough handling of the film roll.
Until now, efforts to reduce film telescoping have primarily involved restricting or reducing the levels of liquid additives, experimenting with winder speed and other process conditions, and varying the type of resin used to produce the film.